Figure 4 Disassembly Of The Control Unit - Motorola Spectra Service Manual

processor to the display driver. When the clock line is
held low for more than 600 mSec, the display driver
resets and new display data follows.
17. Voltage Supply
The ac voltage present on Q23 of the controller
board is used to obtain the -10 volts needed to run the
display driver IC. This voltage is fed through L101 to
limit the current, and then rectified by CR107 and shunt
regulated by CR108.
18. Status LEDs
These LEDs are driven by the display driver as
though they were decimal points on the VF display.
Level shifting transistors are required for this since the
display driver uses 39 volts for control signals.
19. Backlight LEDs
The same microprocessor signal that turns the VF
power supply on and off also operates the backlight
LEDs. Q120 supplies base current to the individual LED
driver transistors. The driver transistors act as constant
current sources to the LEDs. Backlight LEDs CR115,
GPW-3017-A PICK UP FROM PG. 12
Figure 4. Disassembly of the Control Unit
CR116, CR117, and CR118 are connected to thermistor
R163 by way of Q108. This circuit allows more current
to flow through these LEDs at room temperature and
reduces current as the temperature rises.
C. Control Unit Maintenance
1. Disassembly of Control Unit (see Figure 4)
Before disassembling the control unit, note the loca-
tion of the labeled buttons.
Remove the two 30mm slotted screws that hold the
front and back of the control unit together. The two
halves separate at the top; at the bottom, they are
held together by the flex cable that interconnects the cir-
cuit boards. Place the unit so that the PC boards are
facing up.
Remove the five 8mm screws in the display board
and carefully remove the front of the control unit hous-
ing. Keep the front housing parts as a complete unit
(including the front housing, buttons, and display board
light pipe). Always keep the front of the display housing
face down when handling.
NOTE
15